The present invention relates to a motor control system for a sewing machine in which thyristors are employed for motor driving control. More particularly, the invention relates to a system for controlling the "halt" or stop position of the sewing needle of a sewing machine.
Nowadays, a sewing machine employes thyristors and their control systems for motor control. Such a system comprises a mechanical, electric or dynamic brake means to stop the motor at any moment so as to stop the sewing needle at a desired halt position. The brake means are energized when the foot controller is released, thereby generating a stop signal. This energization of the brake means produces impact shock and noise, because the motor of the sewing machine rotates at a relatively high speed to operate the sewing mechanism, a braking operations must be accomplished quickly. It is difficult to stop the sewing needle at a predetermined position correctly and smoothly without mechanical shock and noise.
On the other hand, if the needle position detector means were employed and the brake means were energized by the stop signal from foot controller, as well as by the detection signal from the detector means, to halt the sewing needle at a predetermined position, the motor of the sewing machine may be overheated and destroyed if the sewing needle is jammed and the motor stops before the sewing needle comes to the predetermined halt position.